diff --git a/db/migrate/20110818212541_add_identifier_to_existing_invitations.rb b/db/migrate/20110818212541_add_identifier_to_existing_invitations.rb
index 1471552fc..02c2524f0 100644
--- a/db/migrate/20110818212541_add_identifier_to_existing_invitations.rb
+++ b/db/migrate/20110818212541_add_identifier_to_existing_invitations.rb
@@ -1,6 +1,7 @@
 class AddIdentifierToExistingInvitations < ActiveRecord::Migration
+  class Invitation < ActiveRecord::Base; end
   def self.up
-    execute <<SQL
+    execute <<SQL unless Invitation.count == 0
     UPDATE invitations
       SET invitations.identifier = (SELECT users.invitation_identifier  FROM users WHERE users.id = invitations.recipient_id),
           invitations.service = (SELECT users.invitation_service FROM users WHERE users.id = invitations.recipient_id)
@@ -9,7 +10,7 @@ SQL
   end
 
   def self.down
-    execute <<SQL
+    execute <<SQL unless Invitation.count == 0
     UPDATE invitations
       SET invitations.identifier = NULL,
           invitations.service = NULL